Conventionally, stirring devices having various configurations exist. For example, there is a stirring device disclosed in Patent Literature 1. This stirring device includes a stirring tank for housing a stirring object, a ribbon-shaped stirring impeller configured to cause the stirring object to have fluidity within the stirred tank, and a high-speed rotation stirring impeller configured to shear the stirring object.
The stirring object around shearing teeth is pumped out at the time of shearing the stirring object using the high-speed rotation stirring impeller. Unless a sufficient amount of the stirring object is supplemented so as to compensate the pumped out stirring object, the stirring object may not easily flow into an area with the stirring object pumped out therefrom from the surrounding area in some cases. In such a case, a space (hollow space) with no stirring object created around the shearing teeth (or around the high-speed rotation stirring impeller itself) is caused. Accordingly, the shearing blade cannot catch the stirring object and thereby the high-speed rotation stirring impeller runs idle, which may cause a phenomenon of making it hard for the stirring object to be sheared.
This phenomenon is more easily caused when the high-speed stirring impeller rotates at a higher speed. Further, this phenomenon is highly likely to be caused when the stirring object is a high viscosity fluid and a highly thixotropic fluid (a fluid having properties which makes its flow hard to be propagated, such as creamy fluid).
Meanwhile, in the device of Patent Literature 1, no attention is paid on such a problem, and the ribbon-shaped stirring impeller and the high-speed rotation stirring impeller are arranged in random manner, with no organic relationship therebetween. Therefore, the stirring device disclosed in Patent Literature 1 does not cause fluidity within the stirred tank which enables a sufficient amount of the stirring object to be supplemented so as to compensate the stirring object pumped out by the shearing blade, and therefore the problem of pausing a difficulty in shearing due to the space caused around the high-speed stirring impeller still remains unsolved.